1. Field of the Invention
The present invention relates to a fuel injection valve for controlling a needle valve member in the direction of opening of an injection port by the deformation due to the action that a piezoelectric device having a cylindrical body thereof is installed to a valve body in the condition that a positive or negative voltage is applied and the voltage changed-over to a negative or positive voltage is applied at a fuel injection time.
2. Description of the Prior Art
A conventional fuel injection valve (Japanese Pat. application 2-112663) was constituted as shown in FIG. 7, illustrating that a needle valve N is co-axially interposed in a valve case C having an injection port O, a spring B is also interposed between the needle valve N and a valve cover F, and a hollow cylindrical piezoelectric device P shown in FIG. 8 is installed coaxially with the needle valve N between a shoulder portion S of the needle valve N and a point E of the valve case C without applying any voltage.
Since the fuel injection valve described above was interposed between the needle valve N and the valve case C and accordingly the hollow cylindrical piezoelectric device P was used, there was the disadvantage that cracks occur due to the repetition of expansion and contraction, resulting in disruption and a shortening of the service life in case there is any flaw due to the process and molding on the inner surface thereof.
In addition, since at the time of fuel injection the fuel injection valve described above injects fuel from the injection port 0 by applying, for example, a positive voltage on the piezoelectric device P and accordingly by moving the needle valve N axially and to the left on FIG. 7 while expanding axially in accordance with the positive voltage applied against the spring force by a spring B, there were the disadvantages that an insufficient amount of fuel injection can be achieved because of a small amount of deformation in the piezoelectric device P and it is necessary to make the axial length thereof significantly long by increasing the number of layers of piezoelectric elements in order to obtain the full stroke in the needle valve N, resulting in making the fuel injection valve long.